Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden and does well: it discloses statelessness ("you pass the time you last looked, we compare it against our probe record"), exact price and rail, and that no account or API key is needed. It still does not say what constitutes a change or how staleness/probe freshness affects the answer.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The core purpose sentence is buried third behind a pricing block, so it is not front-loaded. "No account, no API key, no invoice" and "No account and no subscription to administer" are redundant restatements of the same point.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 2-parameter, no-output-schema tool, the payment mechanics are covered, but the description omits what the response contains (changed true/false, timestamp granularity) and any limits on how far back the 'moment you name' can be. Adequate but with clear gaps given no output schema exists.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so both `target` and `payment` are already documented in the schema. The description restates the omit/ supply payment behavior rather than adding new syntax or format detail, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific resource and question: "Has this endpoint changed since a moment you name." The verb/resource pairing is clear and distinct from siblings like liveness_history or new_services. The interleaved pricing preamble delays the core purpose, and it never defines what 'changed' means (content, status, hash).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives procedural guidance for the two-step x402 flow: call without `payment` to get requirements, call again with `payment` to be served. However, it offers no guidance on when to choose this over siblings such as get_weekly_changes, new_services, or uptime_history, so the routing decision is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.